SharePoint 2013 People Picker error: “Sorry, we’re having trouble reaching the server.”

I have had a strange error today in my dev lab environment. First I recognized that I could not select users from the People Picker:

Sorry, we’re having trouble reaching the server.

Second I realized that I was not able to use any function that belongs to WCF web services such as the SharePoint REST API, e.g. at http(s):///_api/web.

Using Fiddler I found this behavior:

HTTP 404 NOT FOUND on /_vti_bin/client.svc/ProcessQuery

Same for /_vti_bin/client.svc/web which is the same as /_api/web.

Search the web I found some hints regarding this error in SharePoint. But nothing worked.

• http://sharepoint.stackexchange.com/questions/71367/sharepoint-2013-restful-calls-returning-404-not-found

• http://stackoverflow.com/questions/17298197/sharepoint-2013-restful-calls-returning-404-not-found

Than I created a own web service “service1.svc” with a simple method in it and placed it in folder \isapi where the virtual folder “_vti_bin” is located on the file system.

Result:  I could not call my own web service too. Same result: NOT FOUND.

Than I search the web for “WCF 404” and found some hints to “HTTP Activation” feature of Windows Server OS. Of course this was activated for .NET 3.5 and .NET 4.5.

• http://stackoverflow.com/questions/11116134/wcf-on-iis8-svc-handler-mapping-doesnt-work

So I deactivated the “HTTP Activation” feature of .NET 3.5 and .NET 4.5 and re-enabled one by one (1st .NET 3.5, 2nd .NET 4.5 ) them after deactivation.

After that I did a IISRESET. – Than everything works again as expected. :-)

and